here's the location of the bigger pic: http://www.tackleunderground.com/photos/index.php?n=2258
in contradistinction to all that has been said... has anyone looked at the Jackall Giron? its practically the same dimensions of the problem bait here. the only variations between the Giron and the non-swimmer are the size/material of the fins and the # of joints (and possibly the width of the lure as well as the exact weighting, but those are difficult to observe from a single side shot lol). the Giron is lacking the ventral depth/elongation, yet it swims... it has an extremely thin head and body width, yet it swims... it has rigid fins (not too big) and yet it swims...
my guess, like others have already made, is that the fins are causing too much drag - just cut 'em down a little, or a lot lol